Inflammatory bowel disease (IBD) is associated with increased levels of lipid mediators of inflammation: leukotriene B4, prostaglandin E2 (PGE2), and platelet activating factor (PAF). In this proposal we will study the interactions between intestinal epithelial cells and two lipid mediators of inflammation, PGE2 and PAF. One of these mediators, PGE2, downregulates the inflammatory response and protects the epithelium. Whereas the other, PAF, is proinflammatory and increases paracellular permeability. Caco-2 cells, a human intestinal epithelial cell line, produce PGE2. Moreover, tumor necrosis factor, a cytokine present in inflammation, induces Caco-2 cells to make more PGE2, by inducing the synthesis of cyclooxygenase. Caco-2 cells also make and secrete acetylhydrolase, an enzyme that degrades PAF. Prolonged exposure to PAF increases the secretion of acetylhydrolase by Caco-2 cells. Thus intestinal epithelial cells appear to actively respond to inflammation by synthesizing a protective lipid mediator, PGE2, and by secreting an enzyme that degrades a destructive lipid mediator, PAF. The central hypothesis behind this proposal is that epithelial cells play an important role in the regulation of intestinal inflammation in IBD. We focus on two aspects of this hypothesis: 1. PGE2 synthesized by intestinal epithelial cells in IBD is protective and its synthesis is enhanced by the induction of cyclooxygenase by inflammatory cytokines. 2. PAF is a proinflammatory mediator in IBD and contributes to the increased paracellular permeability. The effects of PAF in IBD are diminished by its degradation by acetylhydrolase released, in part, by epithelial cells. The specific aims are: 1. To characterize the synthesis and metabolism of lipid mediators by epithelial cells. The cell populations to be studied are Caco-2 cell monolayers and epithelial cells isolated from human colonic surgical resections from normals and IBD patients. 2. To characterize the regulation of cyclooxygenase and acetylhydrolase synthesis by cytokines and inflammatory mediators in intestinal epithelial cells. 3. To characterize the production and degradation of PAF by colonic mucosa and isolated epithelial cells from patients with IBD and normal controls. 4. To characterize the intracellular messengers involved in the regulation of paracellular permeability by PAF. Significance: These studies should provide insights into the role of epithelial cells in the normal regulation of the inflammatory response and into potential abnormalities of regulation in IBD.